Japanese unexamined patent application publication No. JP-A-2000-1010 describes a related art double-sided inkjet image forming apparatus. The related art double-sided inkjet image forming apparatus is configured to form images on both surfaces of a recording sheet. In the related art double-sided image forming apparatus, the recording sheet fed from a sheet feed tray is conveyed along a transfer path, and an inkjet head discharges ink onto the recording sheet while the recording sheet is conveyed. Accordingly, an image is recorded on one surface (e.g., a front surface) of the recording sheet. The double-sided image forming apparatus switches back and conveys the recording sheet and discharges ink from the inkjet head to the recording sheet while conveying the recording sheet. In this way, the double-sided image forming apparatus records an image on the other surface (e.g., a rear surface) of the recording sheet. The recording sheet having images formed on both surfaces is then discharged to a sheet discharging tray.
The related art double-sided image forming apparatus is provided with a unit for drying ink droplets adhered to the surface of the recording sheet.
The related art inkjet image forming apparatus discharges the recording sheet having an image formed on the front surface thereof to the outside once. Then, the related art inkjet image forming apparatus determines whether a dry time has elapsed after image forming on the front surface has been completed. The dry time allows the ink droplets adhered to the front surface of the recording sheet to dry, and depends on the amount of ink adhered to the front surface of the recording sheet. If it is determined that the dry time has elapsed, the recording sheet is fed into the apparatus again, and an image is formed on the rear surface of the recording sheet.
However, the time required to dry the ink droplets adhered to the front surface of the recording sheet depends on many factors, such as the kind of recording sheet, temperature, and humidity as well as the amount of ink adhered to the recording sheet. Therefore, the related art inkjet image forming apparatus has disadvantages in that the dry time is difficult to set, and if the dry time is incorrectly set, a recording sheet is fed again without being completely dried or a recording sheet is not fed again even though the recording sheet has been completely dried. The incorrect dry time thus results in bleed-through on the sheet which has not dried and resulting degradation of image quality, or an increased printing time for the double-sided sheet.